Get the exterior of cell union

[iskandari]

Given a union of s2 cells that originate from GetCovering(), is it possible using the s2 API (in python or go) to obtain the exterior geometry or loop of this union (assuming the union forms a polygon) ?

s2_cells = coverer.GetCovering(s2_polygon)
print(s2_cells[0:5])

(<s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId *' at 0x12fcf3120> >, <s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId *' at 0x12fcf2e80> >, <s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId *' at 0x12fcf3690> >, <s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId *' at 0x12fcf3d80> >, <s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId *' at 0x12fcf2940> >)

cell_union.Init([cell.id() for cell in s2_cells])

#unsure where to go from here

I have tried with a buffering operation but it seems only to return True/False

opts = s2.S2BufferOperationOptions()
opts.set_buffer_radius(s2.S1Angle.Degrees(0.001))
result = s2.S2Polygon()
layer = s2.S2PolygonLayer(result)
op = s2.S2BufferOperation(layer, opts)
for cell in s2_cells:
    op.AddPolygon(s2.S2Polygon(s2.S2Cell(cell)))
op.Build()
#True

I love using s2 and would be grateful for any suggestions on how to obtain the exterior of a covering!

[smcallis]

Is this the python API? The C++ has S2Polygon::InitToCellUnionBorder: https://github.com/google/s2geometry/blob/master/src/s2/s2polygon.h#L594

On Wed, May 1, 2024 at 10:25 PM Alexander Tedeschi @.***> wrote:

Given a union of s2 cells that originate from GetCovering(), is it possible using the s2 API (in python or go) to obtain the exterior geometry of this union ?

s2_cells = coverer.GetCovering(s2_polygon)print(s2_cells[0:5])

(<s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId ' at 0x12fcf3120> >, <s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId ' at 0x12fcf2e80> >, <s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId ' at 0x12fcf3690> >, <s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId ' at 0x12fcf3d80> >, <s2geometry.S2CellId; proxy of <Swig Object of type 'S2CellId *' at 0x12fcf2940> >) cell_union.Init([cell.id() for cell in s2_cells])

unsure where to go from here

I have tried with a buffering operation but it seems only to return True/False

opts = s2.S2BufferOperationOptions()opts.set_buffer_radius(s2.S1Angle.Degrees(0.001))result = s2.S2Polygon()layer = s2.S2PolygonLayer(result)op = s2.S2BufferOperation(layer, opts)for cell in s2_cells: op.AddPolygon(s2.S2Polygon(s2.S2Cell(cell)))

I love using s2 and would be grateful for any suggestions!

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[iskandari]

Looking for a pythonic solution but will try the C++ method!